Define angle of contact?

In general, the surface of a liquid near the plane of contact with another medium is curved. The angle of contact refers to the angle formed by a tangent to the liquid surface inside the liquid. It is denoted by the symbol θ. At the interfaces of different couples of liquids and solids, it is varied. The value of θ determines whether a liquid will spread or form droplets on the surface of a solid.

What is surface tension?

Surface tension is a feature of a liquid surface that manifests itself as a stretched elastic membrane. The roughly spherical shape of little liquid drops and soap bubbles are examples of this phenomenon. Certain insects can stand on the surface of water due to this characteristic. The surface tension of water may also support a razor blade. The razor blade does not float; if pushed through the water’s surface, it sinks.

What is the angle of contact of water?

The angle of contact is 0° for pure water and thoroughly clean glass. It is between 8° and 18° for regular water and glass. The angle of contact between pure water and pure silver is 90 degrees. The surface of pure water is flat when it is placed in a pure silver vase.

Define surface tension and angle of contact?

The force per unit length operating at right angles to an imaginary line drawn on the liquid’s free surface is known as surface tension. When a liquid comes into contact with a solid, the angle of contact is defined as the angle between the tangent drawn to the free surface of the liquid and the surface of the solid at the point of contact measured inside the liquid.

What is the source of Pepper's aversion to soap?

Pepper is hydrophobic, which means it will not dissolve or mix in water. The pepper stays afloat because water molecules are strongly attracted to each other or have high surface tension. When soap is added, the surface tension is reduced, and the pepper is carried away by the water molecules as they spread away from the soap.

Angle of Contact – Definition, Importance and Characteristics

By BYJU'S Exam Prep

Updated on: September 25th, 2023

The angle of contact is determined by the composition of the liquid, the solid in contact, and the medium above the liquid’s free surface. Before we define the angle of contact, let’s define surface tension first. Any liquid’s surface tension is a trait that causes it to try to minimize its free surface area. The force operating per unit length on an imaginary line drawn tangentially on the free surface of a liquid is known as surface tension. The angle formed by the meniscus and the enclosing walls of a liquid column when measured from the vertical wall beneath the liquid’s surface to the position of the tangent to the meniscus at its point of contact with the wall.

The liquid and solid characteristics in contact and the medium above the liquid’s free surface determine the angle of contact. A glass capillary tube becomes water-proof when the wax is applied to it. The contact angle widens and becomes obtuse. It does not hold water. Instead, the obtuse angle of contact causes it to descend into the tube. Here we will see the definition of contact angle, the factors which the angle of contact depends upon and the characteristics of the angle of Contact.

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Table of content

1. What is the Angle of Contact?
2. Definition of Angle of Contact
3. Importance of Angle of Contact
4. Characteristics of Angle of Contact

What is the Angle of Contact?

The angle of contact is defined as the angle subtended between the tangents drawn at the liquid surface and the solid surface inside the liquid at the point of contact. The angle of contact is defined as the angle subtended between the tangents drawn at the liquid surface and the solid surface within the liquid at the point of contact or as the angle subtended between the tangents pulled at the liquid surface and the solid surface within the liquid at the point of contact.

The composition of the liquid, the solid in contact, and the medium above the liquid’s free surface all influence the angle of contact. The angle of contact increases as the temperature of the liquid rises. The angle of contact decreases when soluble pollutants are added to a liquid.

Definition of Angle of Contact

“It is defined as the angle subtended between the tangents drawn at the liquid surface and the solid surface inside the liquid at the point of contact.”

As the temperature of the liquid rises, so does the angle of contact.
When soluble impurities are added to a liquid, the angle of contact decreases.

The angle of contact depends upon

Medium above the liquid’s free surface.
Liquid’s characteristics
Solid in contact

Importance of Angle of Contact

The angle of contact between the surface of the solid and the tangent drawn to the free surface of the solid and the tangent drawn to the free surface at the point of contact measured inside the liquid is defined as the angle between the surface of the solid and the tangent drawn to the free surface of the solid and the tangent drawn to the free surface at the point of contact measured inside the liquid. The contact angle controls whether a liquid will spread or form droplets on a solid’s surface.

If the contact angle is obtuse, a droplet will be created.
If the contact angle is acute, the water will spread.

Characteristics of Angle of Contact

The following are the features of contact angle: It is constant for a certain liquid-solid pair and is determined by the sort of solid that comes into contact with the liquid. The rest of the parameters remain unaltered. The angle at which the solid touches the liquid surface has no bearing on it. It is affected by surface tension. As the surface tension varies, the temperature and purity of the liquid fluctuate. The medium above the liquid’s free surface determines it.

Property	Angle of Contact <90 Degree	Angle of Contact = 90 Degree	Angle of Contact >90 Degree
Substance	Water and Glass	Water and Silver	Mercury and Glass
Meniscus Shape	Concave	Plane	Convex
Capillary Action	Liquid Rises	No Effect	Liquid Falls
Sticking to Solid	Wet	Does not wet	Does not wet
Liquid Surface’s Shape	Almost Round	Spreads Across the Surface	Flat

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